1. Field of the Invention
The present invention relates to a turbine rotor having blades of composite ceramic material.
The search to improve performance in modern turbine plant, particularly in the aeronautical field, has led to a constant rise of working temperatures, particularly the temperatures at the turbine inlet. These operating conditions have brought about technical design developments, covering in particular arrangements concerned with cooling in order to obtain an acceptable service life of the mechanical parts forming the turbine, particularly those parts most exposed to the flow of hot gases, such as the turbine rotor blades. A parallel stream of developments has also taken place in the perfecting of new materials having improved resistance to high temperatures while meeting the demands of the mechanical or aerodynamic operation. Along these lines attempts have been made at using various composite materials, particularly those based on ceramic fibres. Several examples illustrate these known techniques.
2. Summary of the Prior Art
French Pat. No. 2176350 relates to a composite blade and describes a particular method of tibre distribution and of their arrangement for the transition from the aerofoil portion of the blade to its root, which may be, for example, of dovetailed shape.
French Pat. No. 2154050 relates to a method of constructing a turbine blade of which the aerofoil portion of the blade is composed of fibre reinforced layers, and the root has hardened wedges inserted between the layers.
French Pat. No. 2538029 describes ceramic blades having a metal core surrounded by a covering of refractory ceramic, and including air flow and inner cooling arrangements associated therewith. A flared root of the blade is rigidly secured to the central core by a securing pin.
West German Pat. No. 830854 describes a ceramic blade of which the bulb of the root has an angle of convergence between the sides limited to a value deduced from the characteristics of the material, particularly from the ratio of the admissible compressive and tensile stresses.
However, none of the known arrangements is completely satisfactory. Indeed, either the presence of metal parts in the blade causes the loss of the chief advantages to be obtained from the use of composite materials, or very complex fibre arrangements are demanded which cause manufacturing difficulties in the arrangement of the fibres or fabrics, both in the transition from the aerofoil portion of the blade to its root and in the shaping of the root, or also in the transition from the aerofoil portion to the platform of the blade.
The object of the present invention, therefore, is to provide a turbine rotor having blades of the above-mentioned type which avoids the drawbacks associated with the previously known solutions.